The invention relates generally to a miniaturized electronic device, of the type comprising a substrate one surface of which carries by a first pattern of metallic elements of an electrical circuit and a second pattern of metallic elements of an electrical circuit which are crossing each other at least at some places, the crossing electrical circuit elements being separated by a dielectric material.
As in other fields of electronic devices, one also seeks to reduce the sizes of the devices of the kind which has just been mentioned with the purpose of obtaining ultra-miniature structures which may work at frequencies higher than 3 GHz. One in particular endeavours to provide devices with a gyromagnetic effect: such as circulators or isolators which comprise three inductances angularly offset by 120.degree. on the substrate, these inductances forming the aforesaid patterns of electrical circuits. It is advantageous that in such devices the inductances lie between a lower substrate and an upper substrate the outer surfaces of which are metallized or sprayed with a metal.
In particular two major problems are opposing an ultra-miniaturization, namely the problem of the electrical earthing connection of both metallic layers and the configuration of the inductances and the one raised by the parasitic capacitances resulting therefrom.
As to the problem of these inductances, two solutions have been proposed which however have proved to be insufficient. Thus the inductances or in a more general manner the patterns of electric circuits have been provided in a same plane by providing conducting bridges at the crossing spots of the electrical conductors. This structure did not lead to the ultraminiaturization sought of the device. Another solution consists in providing the patterns of electrical circuits in two different planes electrically insulated by an interposed dielectric and to provide within the dielectric holes permitting suitable circuits elements to be connected. This approach came up heretofore against the impossibility to provide holes with small diameters and with the required accuracy for carrying out the miniaturization. This technological problem is all the more awkward as the thickness of the dielectric increases, which would however be advantageous in some cases of application for example to reduce the spurious capacitances and to increase the operating frequency.